Amplifying system



0a. 16-, 1928. Re. 17,105

' A. CROSSLEY AMPLIFYING SYSTEM Original Filed OV- 10, 1925 l INVENTOR.

A TTORNEY Reissued Oct. 16, 1928.

UNITED STATES" PATENT OFFICE.

ALFRED CBOSSLEY, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOB T0 WIRED nnmo,

INC., 01? NEW YORK, N. Y., A CORPORATION OF DELAWARE.

Amrmrrmo svs'rnm.

Original No. 1,651,810, dated December 6, 1927, Serial No. 68,121, filed November 10, 1925. Application for reissue filed December 23,

My invention relates broadly to radio transmitting systems and more particularly to means for eliminating self-oscillations in the circuits of radio transmission systems.

One of the objects of my invention is to provide a constant frequency controlled electron tube transmission system in which maximum energy is impressed upon an antenna ground system without losses occasioned by self-oscillations normally present in the electron tube circuits of a radio transmitter.

Another object of my invention is'to provide means for connection in the plate lead close to the plate terminal of an electron tube amplification system of a radio transmitter for eliminating high frequency self-oscillations in the amplification system with negligible effect on the amplifier output at the required frequency.

Still another object of my invention is to provide an arrangement of radio transmission system in which a piezo-electrical crystal controlled oscillator is connected with an electron tube amplification system for impressing high frequency oscillations upon the electron tube amplification system without loss in the amplification system arising out of the generation of self-oscillations which normally tend to reduce the radiation of the transmission system.

A further object of my invention is to pro vide an electrical circuit arrangement for a high frequency electron tube amplification system in a radio transmitter wherein a resistance is connected in series with the plate lead of the amplifier and close to the plate terminal thereof and connected in series with the high frequency resonance circuit of the amplifier for increasing the resistance of the circuit to such an extent that the regenerative property of the grid-plate capacity is not sufiicient to cause oscillations.

M invention will be more fully understoo from the specification hereinafter following by reference to the accompanying drawings wherein in Figure 1, my invention is illustrated as applied to the high frequency power amplifier system of a piezoelectric crystal controlled oscillator showing the means which I provide for eliminating self-oscillations in the amplification system; and Fig. 2 shows my invention in connection with a modulation circuit in a transmitter plate inductance coil systems.

The output circuit 1927. Serial N0. 242,261.

apparatus employed in a. wired radio broadcasting system.

In the development of piezo-electric crystal controlled transmitters, I have found that serious difliculty is encountered in connecting a power amplifier with the piezo electric crystal controlled oscillator by the presence of self-oscillations in the various stages of amplification. .This diflicult'y is aggravated by the use of electron tubes which have low plate impedance and high inter-electrode capacities. The self-oscilla-' tions in the electron tube amplifier system of a radio transmitter are of a high frequency nature and may be attributed to the inductance of the grid and plate leads together with the inter-electrode capacities and distributed capacity of the choke and I have discovered a method for eliminating the selfoscillations as set forth in detail in the drawing, where reference characters 1 and 2 designate an antenna ground system inductively connected to an oscillatory circuit I with the oscillatory output circuit containing inductance 6 and capacity 7 of the os cillatory tube 8. The grid electrode 5" of tube 5 is properly biased by means of battery 31. The input circuit of the oscillatory tube .8, between grid electrode 8 and filament electrode 8*, includes the piezo-electric crystal 9 connected between metallic plates 10 and 11 which connect respectively with grid electrode 8", and filament electrode 8.

The filament electrode 8 is heated from battery 12 under control of rheostat 14. The input circuit of the oscillator tube 8 is shunted by means of a series circuit includ; ing source of potential 15 in series with radio frequency choke 16 by which a negative potentialis impressed upon grid electrode 8" and the piezo-electric crystal control circuit is operated at substantially no load. of the oscillator tube 8 contains the radio frequency choke coil 17 and high potential battery 18 for supplying the positive potential to the plate 8. Condenser 19 is mterposed in the plate lead in series with the oscillatory circuit containuctance 6 and condenser 7.

tube has its filament 5 I provide a radio frequency choke coil 22 and a source of high potential 23 shunted by a radio frequency by-pass condenser 24. Condenser 25 is interposed in series withan oscillatory system 34 which connects with the radiating circuit. I find that by inserting a resistance 26 in the plate lead of the tu e 5 close to the plate terminal 5 that high frequency self-oscillations are prevented with negligible efl"ect on the amplifier output at the required frequency. It will be noted'that the resistance 26 is connected immediately adjacent the terminal of plate electrode 5 at which point it is most efiective in the circuit. The resistance 26 is also arranged in series with the high frequency resonance circuit 3-4 and with the radio frequency choke coil 22 in the high potential circuit. The high frequencvresonance grid and plate electrodes and between the grid and filament electrodes. The resistance 6 is positioned directly in the high frequency circuit in such manner that it carries all of the h' h frequency current. f

frequency oscillations is due to the capacity between grid and plate of the tube which is of a fixed value, it can be assumed that any means used to increase the resistance of the high frequency circuit will affect the feed back qualities of the circuit. It is therefore possibl' circuit that th e feed back qualities of the gr1d-plate capacity are not suflicient to cause oscillations. By the circuit arrangement of the present invention I completely eliminate the undesired frequency oscillations.

output at the resistance has plate circuit impedance.

' resistance to the impedance of various tubes .'full effect of the now employed in high power transmitters l varies from one part in thirty,-to one part in one hundred when we consider the :oper

ating or dynamic impedance of such tubes.

The

7 power amplifier 5.

' voice e to so increase the. resistance of'the' small value compared with the The ratio of this lations upon the radiating circuit and thereby greatly increase the eificiency of the transmission system.

In Fig. 2 I have shown my invention as applied to a broadcasting transmitter system for wired radio operation where a line wire system 41 is ,p quency carrier currents impressed thereon through inductance 30 and tuningcondenser 40, where theinductance 30 is coupled with the inductance 3 inthe output circuit of the The oscillator 8 is controlled by piezo-electric crystal 9 as described in connection with Fig. 1. A modulator tube 32 is connected across the power amplifier circuit as shown, where a low frequency choke coil 34 i is introduced in the output circuit of the power amplifier tube 5 in series with the high potential battery 23.

The modulator tube is controlled through audio frequency transformer 37 having primary winding 36 and secondarywinding 35.

he primary winding is connected in the controlcircuit including battery source 39 and microphone 38. The constant frequency oscillations under control of the piezoelectric crystal 9 are impressed upon the line wire system 41-and modulated from microphone 38.

While-I have shown preferred circuit arrangements, it will be understood that the principle of my invention may be applied to various combinations of circuits and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims. l

hat I claim and desire to secure by Letters Patent of the United States is as folas the feed back which causes undesired high 1 tubes having its input circuit coupled with transmission sysplurality of electhe output circuit of said first mentioned electron tube, the output circuit of said last mentioned tube including parallel branch the circuits thereof. v g I 2 In a high frequency transmission system the combination ofa plurality of elec tron tubes, having grid, filament and plate electrodes, input and output circuits interrovided and high frecircuits, and a resistance connected'in series connecting said electrodes, a piezoelectric crystal connected in the input circuit of one of said electron tubes for controlling the generation of oscillations in the circuit of said electron tube, another of said electron tubes having its input circuit coupled with the output circuit of said first mentioned tube, the output circuit of said last mentioned electron tube comprising a pair of branch circuits, one branch circuit including oscillatory elements and another including a high potential source, and a resistance connected in series with each of said branch circuits and directly connecting to the terminal of the plate electrode of said last mentioned electron tube, whereby said electron tube operates as a power amplifier at the frequency of said piezo-electric crystal,- while undesired selfoscillatory currents are eliminated.

3. A piezo-electric crystal controlled transmission system comprising a piezo-elec'tric crystal element capable of producing constant frequency oscillations, an electron tube circuit for sustaining said oscillations, an

' electron tube power amplifier system connected to said electron tube circuit, a modulatiorrcircuit comprising an independent elecincreasing the amplitude of said oscillations a modulation circuit comprising an electron tube having its plate and filament electrode conductively connected across the output ci'rcuit of said power amplifier, and a resistance interposed in the connection between the plate electrode of said power amplifier and the plate electrode of said modulation circuit for preventing reaction of said power amplifier and modulation circuit upon said piezo-electric crystal element.

ALFRED OROSSLEY. 

